The PDP-15 was an

18-bit Eighteen binary digits have 262,144 (1000000 octal, 40000 hexadecimal) distinct combinations. Eighteen bits was a common word size for smaller computers in the 1960s, when large computers often using 36 bit words and 6-bit character sets, som ...

minicomputer A minicomputer, or colloquially mini, is a type of general-purpose computer mostly developed from the mid-1960s, built significantly smaller and sold at a much lower price than mainframe computers . By 21st century-standards however, a mini is ...

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...

that first shipped in February 1970. It was the fifth and last of DEC's 18-bit machines, a series that had started in December 1959 with the

PDP-1 The PDP-1 (Programmed Data Processor-1) is the first computer in Digital Equipment Corporation's PDP series and was first produced in 1959. It is known for being the most important computer in the creation of hacker culture at the Massachusetts ...

. More than 400 were ordered within the first eight months. A later model, the PDP-15/76, was bundled with a complete

PDP-11 The PDP–11 is a series of 16-bit minicomputers originally sold by Digital Equipment Corporation (DEC) from 1970 into the late 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of a ...

, allowing the PDP-15 to use peripherals for the PDP-11's popular

Unibus The Unibus was the earliest of several computer bus (computing), bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts, Maynard, Massachusetts. The Uni ...

system. The last PDP-15 was produced in 1979, with total sales of about 790 units. The PDP-15 was essentially a version of the earlier

PDP-9 The PDP-9, the fourth of the five 18-bit minicomputers produced by Digital Equipment Corporation, was introduced in 1966. A total of 445 PDP-9 systems were produced, of which 40 were the compact, low-cost PDP-9/L units.. History The 18-bit PDP ...

that was constructed using

small-scale integration An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components ...

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

s, which made it smaller and less expensive than the PDP-9's

flip chip Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting dies such as semiconductor devices, IC chips, integrated passive devices and microelectromechanical systems (MEMS), to exter ...

s which used individual

transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

s. A basic 8 kW PDP-9 cost about $35,000 in 1968 (), whereas the PDP-15 with 4 kW was only $15,600 () and a fully-equipped system with 8 kW,

punch tape file:PaperTapes-5and8Hole.jpg, Five- and eight-hole wide punched paper tape file:Harwell-dekatron-witch-10.jpg, Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program ...

, KSR-35 terminal, math coprocessor and dual

DECtape DECtape, originally called Microtape, is a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX ...

was $36,000 (), making a complete system significantly less expensive than the earlier machine. In addition to

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s, the PDP-15 has compilers for Fortran and

ALGOL ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...

History

The 18-bit PDP systems preceding the PDP-15 were named PDP-1,

PDP-4 The PDP-4 was the successor to the Digital Equipment Corporation's PDP-1. History This 18-bit machine, first shipped in 1962, was a compromise: "with slower memory and different packaging" than the PDP-1, but priced at $65,000 - less than half t ...

PDP-7 The PDP-7 is an 18-bit computing, 18-bit minicomputer produced by Digital Equipment Corporation as part of the Programmed Data Processor, PDP series. Introduced in 1964, shipped since 1965, it was the first to use their Flip-Chip module, Flip- ...

and

. The last PDP-15 was produced in 1979.

Hardware

The PDP-15 was DEC's only 18-bit machine constructed from TTL

s rather than discrete transistors, and, like every DEC 18-bit system could be equipped with: * an optional X-Y (point-plot or

vector graphics Vector graphics are a form of computer graphics in which visual images are created directly from geometric shapes defined on a Cartesian plane, such as points, lines, curves and polygons. The associated mechanisms may include vector displ ...

) display. * a hardware

floating-point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a Sign (mathematics), signed sequence of a fixed number of digits in some Radix, base) multiplied by an integer power of that ba ...

option, with a 10x speedup. * up to 128K words of core main memory

Models

The PDP-15 models offered by DEC were: * PDP-15/10: a 4K-word paper-tape-based system * PDP-15/20: 8K, added

* PDP-15/30: 16K word, added memory protection and a foreground/background monitor * PDP-15/35: Added a 524K-word fixed-head disk drive * PDP-15/40: 24K memory * PDP-15/50:

PDP-15/76

* PDP-15/76: 15/40 plus PDP-11 frontend. The PDP-15/76 was a dual-processor system that shared memory with an attached PDP-11/05. The PDP-11 served as a peripheral processor and enabled use of

peripherals.

Software

''DECsys'', ''RSX-15'', and ''XVM/RSX'' were the

s supplied by DEC for the PDP-15. A

batch processing Computerized batch processing is a method of running software programs called jobs in batches automatically. While users are required to submit the jobs, no other interaction by the user is required to process the batch. Batches may automatically ...

monitor Monitor or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, Wes ...

(BOSS-15: Batch Operating Software System) was also available.

DECsys

The first DEC-supplied mass-storage

available for the PDP-15 was DECsys, an interactive single-user system. This software was provided on a DECtape reel, of which copies were made for each user. This copied DECtape was then added to by the user, and thus was storage for personal programs and data. A second DECtape was used as a scratch tape by the assembler and the Fortran compiler.

RSX-15

RSX-15 was released by DEC in 1971. The main architect for RSX-15 (later renamed XVM/RSX) was Dennis "Dan" Brevik. Once XVM/RSX was released, DEC facilitated that "a PDP-15 can be field-upgraded to XVM" but it required "the addition of the XM15 memory processor." The

RSX-11 RSX-11 is a discontinued family of multi-user real-time operating systems for PDP-11 computers created by Digital Equipment Corporation. In widespread use through the late 1970s and early 1980s, RSX-11 was influential in the development of later ...

operating system began as a port of RSX-15 to the

, although it later diverged significantly in terms of design and functionality.

Origin of the RSX-15 name

Commenting on the ''RSX'' acronym, Brevik says:

XVM/RSX

Later versions of the PDP-15 could run a real-time multi-user OS called XVM/RSX, an outgrowth of RSX-15. The ''XVM'' upgrade to RSX was multi-user, and enabled up to six concurrent teletype-based users. XVM Support for the PDP-15/76 included using an RK05 disk drive.

non-DEC

The

MUMPS MUMPS ("Massachusetts General Hospital Utility Multi-Programming System"), or M, is an imperative, high-level programming language with an integrated transaction processing key–value database. It was originally developed at Massachusetts Gen ...

operating system, which was originally developed in 1966, was developed on the PDP-7 outside DEC. It is also available for the PDP-15.

Application software

DEC provided mathematical, scientific and commercial software application tools. "Commercial Subroutine Package (CSP) ... compatible with the

IBM 1130 The IBM 1130 Computing System, introduced in 1965, was IBM's least expensive computer at that time. A binary 16-bit machine, it was marketed to price-sensitive, computing-intensive technical markets, like education and engineering, succeeding th ...

commercial subroutine package."

References

External links

a diary re PDP-15 & RSX-15
{{DEC hardware DEC minicomputers 18-bit computers Transistorized computers Computer-related introductions in 1970